This invention relates to an apparatus for pneumatically feeding fiber material to a plurality of carding machines with the intermediary of separate reserve chutes connected to each carding machine upstream thereof as viewed in the direction of material advance. The reserve or upper chutes, in turn, are coupled to a common pneumatic conveyor conduit and advance the fiber material to downstream-connected feed chutes. The fiber transporting conveyor conduit is coupled with an upstream located fiber processing machine, such as a fine opener and contains a fiber-transporting fan.
In a dual-chute card supplying arrangement as disclosed, for example, in U.S. Pat. No. 4,219,289 (issued Aug. 26, 1980) the filling conditions in the upper chute (reserve chute) are not allowed to greatly deviate from the desired normal conditions if a satisfactory uniformity of the fiber lap, as concerns width and time are to be ensured. It is noted that by "filling conditions" there are meant the material quantities in the upper chute, the compression and distribution of the material as well as the shape and size of the material accumulation on the separating surface. The filling conditions in the upper chute depend, among others, from the tuft-air ratio, the tuft size, the air resistance of the separating surface, that is, the shape and size thereof, the transport speed of the fiber tufts, the rate of air discharge and the velocity of air exit at the separating surfaces. Some of these magnitudes depend from the static air pressure, the air quantities and the velocity in the conveyor ducts (transport conduits) leading to the feed chutes. These last-named parameters, in turn, are determined by the operating point of the upstream-connected fan and the filling conditions at the separating surfaces of all downstream-arranged upper feed chutes as well as the geometry of the transport conduits. If fluctuations are maintained within certain narrow limits, satisfactory results can be obtained. The magnitudes of fluctuation are determined by the number of momentarily operating (that is, fiber-consuming) carding machines, the momentary flow rate of material per location, the extent of fiber opening performed on the material supplied to each location as well as the gliding properties and the air resistance of the material. Upon output fluctuations at the individual carding machines, as well as by starting and stopping the carding machines and by density fluctuations in the fiber supply, determined by an upstream-connected cleaning line, the filling conditions often change beyond permissible limits. It is necessary to perform modifications at a number of locations in order to adapt the filling conditions to the changed conditions of the material and the number of the connected carding machines. This is effected in practice usually only during a new setting of the equipment and involves significant expense. Despite such measures there remain, even during a preselected and desired operational condition of a fiber processing system, fluctuations of the filling conditions which are caused by changes during operation. Thus, in the case of each individual carding machine the output speed may change, for example, during coiler can replacement, operational disturbances, verifications, and the like or in case strongly fluctuating material quantities are supplied by the feeding fan into the conveyor duct system which feeds the upper feed chutes (reserve chutes).
In a known apparatus the basic speed of the fiber transport fan is set upon the first production of a predetermined lot for a given number of cards. Upon change of the lot type or a change of the number of cards, for example, because of retooling, interruption in operation, start or stoppage or the like, belt pulleys have to be replaced in order to change the basic speed of the fan and thus the air quantities and/or air velocities in the transport duct and in the reserve chutes of the card feeders. Such an apparatus has therefore the disadvantage that upon change in the composition of a lot or the number of operating cards, the conditions of air flow in the conveying duct may be adjusted only with a significant input of labor which is very time-consuming and causes long down periods.